1. Field of the Invention
The invention refers to a method for determining parameters of a characteristic of a gas-selective electrode in an automatic liquid analyzing device.
2. Related Prior Art
Automatic liquid analyzing devices with a gas-selective electrode are used, for example, to determine the content of ammonium in waste water. The concentration/voltage characteristic of gas-selective electrodes is always plotted logarithmically. The logarithmic characteristic of gas-selective electrodes typically is linear in the range of medium and high concentrations so that the position and the inclination of the linear portion of the characteristic can be determined by measurements using two standard solutions of different concentration. With concentrations below a limit value, the characteristic is not linear but becomes ever flatter as the concentration decreases. Determining or estimating the non-linear portion of the characteristic is effected by measurements using further standard solutions. This method is cumbersome and, moreover, inexact.
Spent gas-selective electrodes supply inexact measuring results. The degree of electrode wear can only be determined by evaluating the measuring results obtained with the standard solutions, which is inexact.
It is an object of the invention to improve the precision of measurement for measurements taken with a gas-selective electrode in an automatic liquid analyzing device.